No. 150 - First rendezvous manoeuvre
31 January 2011 10:12
Report for the period 17 to 24 January 2011
This report covers 8 days of Rosetta mission operations. During the reporting period about 98 per cent of the first rendezvous manoeuvre (RDVM#1, total DV ~ 780 ms-1) was completed with a sequence of six burns.
During the second planned burn the spacecraft entered safe mode due to a large performance anomaly in the reaction control system (RCS). The spacecraft was promptly recovered and the mission control team at ESOC implemented a new operations strategy for the RCS to mitigate the problem. In view of the problems experienced, the manoeuvre and its split had to be redesigned and was then completed with the use of the redundant thruster set. Spacecraft behaviour was also non-nominal with the use of the new operating mode and the redundant thrusters; however, the replanned burns were completed successfully. The spacecraft is currently in nominal status and on track to perform the final trim manoeuvre (∆V 17.6 ms-1 TBC, about 2 per cent of the total) on 10 February.
During the reporting period, mission operations were conducted using the ESA New Norcia (NNO) ground station and the DSS-24 (Goldstone, 34 metres), DSS-25 (Goldstone, 34 metres), DSS-26 (Goldstone, 34 metres) and DSS-65 (Madrid, 34 metres) NASA Deep Space Network (DSN) antennas.
At the end of the reporting period on 24 January, Rosetta was 598.2 million km from Earth (3.99 AU); the one-way signal travel time was 33 min 16 sec (1996 sec). The spacecraft's distance from the Sun was 583 million km (3.90 AU).
A performance anomaly in the reaction control system (thought to have been caused by thruster 9A) led to an attitude pointing error and then to the spacecraft transitioning to level two safe mode during burn 1B on 18 January. Following a switchover to the redundant thruster set and replanning of the rendezvous manoeuvre, the remaining burns were completed successfully.
The spacecraft trajectory is now being carefully analysed to assess the exact performance of the bulk of the first rendezvous manoeuvre. Once this assessment is complete, the trim manoeuvre, planned for the 10 February with a nominal ΔV of 17.6 ms-1 will be finalised in terms of magnitude and direction. Any remaining residual errors will be cleared with a second trim manoeuvre in March.
Summary of upcoming events: